Just now got back from the beach, pulled in the driveway and went into the house and all was well. So I walk back outside and the front top center clearance light lens on the coach is hanging at 90 degrees. Had the same event happen with a different top center lens over the summer after pulling into the campground after a 450 mile ride.

Twice lucky, but I don't count on a third..

Big question, anyone find a replacement lamp that will fit the existing drilled holes? LED maybe?

Smaller question, what is the preferred adhesive to keep the lens on while still servicable for the bulb?

You should not need any adhesive to hold the lens on...should just snap on and stay. If adhesive is needed, you probably need new lights. The ones that come with your rig, like my Lexi are el-chepo's.
I replaced mine shortly after I got it. Went to led's, round. Replaced all 10 in front/rear. Holes on new lined up with old.
Just google up "led clearence lighting"....many sights will come up. Just go to a reputable site and find one with same shape/diameter.
When I installed the new ones (like 5 years ago) I put a dab of Dicor over each hole before I screwed the light down. Still tight and dry.
Grumpy